The present invention relates to a method of and an apparatus for controlling the pH of culture solution for a living organism.
It is quite important to control pH in the culture of a living organism such as in hydroponics. Such method has hitherto been used as neutralizing by adding alkali or acid into a culture solution tank from storage tanks. The amount of alkali or acid to be added is based on the measurement with a pH meter. When automatic control is required, the storage tanks for alkali and acid are provided with electrovalves which control the release of the contents, and the electrovalves are driven by a controller which works responsively to the signal from the pH meter having an electrode inserted into the culture solution.
Such method, however, has not been satisfactory for reasons as follows:
A desirable value of a pH of the culture solution is in a narrow range near neutrality. Therefore when concentrated alkali and acid is used, it is difficult to maintain pH in the desirable range because pouring thereof easily causes large change of pH. To accurately control a pH, it is desirable to use dilute alkali and acid. The use of dilute alkali and acid requires large tanks for storing them. Further it is necessary to supplement alkali or acid in the storage tanks frequently. Further the electrovalves for the tanks must be corrosion-resistant because alkali or acid flows therethrough. Further, the case possibly occurs that alkali solution reacts with CO.sub.2 gas in air to make carbonate, and it enters into the culture solution through neutralization, resulting in bad effect on plants, or it chokes up the gateway by solidifying.